A light emitting diode (LED) is rapidly expanding its market for a backlight of a liquid crystal display (LCD) and for lighting in automotive applications such as headlight because of a low power consumption, a long life time and design against the background of significant improvement in luminous efficacy. In the future, the LED is expected to form an enormous market also in the general lighting field because of a low environmental burden.
An emission color of an LED is limited since an emission spectrum of the LED depends on a semiconductor material for forming the LED chip. Therefore, in order to obtain LCD backlight or white light for general lighting by using an LED, it is necessary that a phosphor suitable for an LED chip is arranged on the LED chip to convert an emission wavelength. Specifically, a method of disposing a yellow phosphor on an LED chip to emit blue light, a method of disposing a red phosphor and a green phosphor on an LED chip to emit blue light, and a method of disposing a red, a green and a blue phosphors on an LED chip to emit ultraviolet light are proposed. Among these methods, the method of disposing a yellow phosphor on an LED chip to emit blue light, and the method of disposing a red phosphor and a green phosphor on a blue phosphor are currently most widely employed from the viewpoints of luminous efficacy and cost standpoints of the LED chip.
For example, Patent Literatures 1 to 2 propose a method of dispersing a phosphor in a liquid resin for encapsulating an LED chip as a specific method of disposing a phosphor on an LED chip. However, when the dispersion of the phosphor in the liquid resin is nonuniform, color deviation is produced with respect to each chip.
Then, a method of using a sheet-like resin layer (phosphor sheet) in which a fluorescent material is previously dispersed uniformly is proposed (for example, Patent Literatures 3 to 8). This method is superior in that a constant amount of a phosphor can be more easily arranged on an LED chip than a method of dispensing a liquid resin, in which a phosphor heretofore put to practical use is dispersed, on an LED chip and curing the resin, and color and brightness of the resulting white LED can be uniform.